This invention relates to an apparatus for sorting out defective plastic crates for containing a plurality of articles such as beer bottles for transportion thereof.
Plastic materials from which such plastic crates (hereinafter referred to most often as "crates") are produced are generally polyethylene, polypropylene and copolymers thereof. However, when these plastics are used for a long period of time, the molecular weight at the surface thereof tends to be reduced particularly by sunlight rays to cause fine cracks, and these plastics tend to become brittle.
Accordingly, when crates made of such plastic materials are used for a long period of time, the strength thereof is gradually lowered and eventually the crates become unusable. More specifically, crates having lowered strength are subject to damage or breakage due to handling and/or stacking during distribution. Further, when a crate breaks on a production line of a bottling factory, the production may be obstructed.
However, no inspection of such crates has been carried out in the past. This is because plastic bottle crates began to be first used around 1965, and only about 16 years have elapsed even for initially produced crates. Therefore, even if the quality of these crates has deteriorated to some extent, their deterioration has not heretofore been of an extent such as to preclude their use.
However, there is a possibility that decrease in strength with long period of use will cause an increase in crates which cannot withstand use. Thus, while there may be a process wherein the crates are inspected or sorted out on the basis of their production years, such a process is not suitable because the strength decrease of the crates varies depending upon the state of use of the individual crates.
While there may be another process wherein the degree of the deterioration of the bottle crates is inspected or detected by the degree of fading of the coloring pigment or the appearance such as gloss of the surface, such a process is unreasonable because the inferiority of appearance is not directly related to strength. Further, such an inspection of appearance is not efficient, and such a process is liable to cause errors.